JP2002084235A - Apd bias voltage control circuit - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an APD(Avalanche Photo Diode) bias voltage control circuit that can combine an optical reception module and an APD bias voltage control section in a general purpose way, downsize the optical reception module by externally mounting the APD bias voltage control section and commonly structure the PIN element optical reception module. SOLUTION: The optical reception section 60 that receives an optical signal input, converts it into an electric signal and outputs output data and the APD bias circuit control section 70 that provides an optimum bias voltage to an APD of the optical reception section 60 are separately configured, and the APD bias voltage control section 70 consists of a DC voltage source 71 that can control its output voltage, a variable resistor 10 for controlling a bias voltage that is connected to the DC voltage source 71 and the resistance of which is varied with an external signal, and a CPU 72 that conducts various controls.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an APD bias voltage control circuit for an optical receiver using an APD (avalanche photodiode) applied to an optical transmission device.

[0002]

2. Description of the Related Art A circuit utilizing a multiplication effect near the breakdown voltage of an APD is used in a portion for converting an optical transmission signal into an electric signal. A conventional method for controlling the APD bias voltage is described below.

[0005] Fixed gain method (fixed bias method) FIG. 5 is a conceptual diagram of a fixed gain method. Here, when the applied voltage is small, a small current substantially equal to the current flowing through a normal photodiode flows, and when the applied voltage increases, a large amount of current flows through the APD near the breakdown voltage. The ratio between the large current and the small current is referred to as a multiplication factor M.

In FIG. 5, reference numeral 51 denotes a DC voltage source for applying a DC voltage to the APD with a reverse bias. A load resistance R0 for I / V conversion is connected to the anode side of the APD. The potential at the connection point between the load resistance R0 and the APD is supplied to a preamplifier (preamplifier) 52.

In this circuit, since the DC voltage applied to the APD has a constant bias voltage regardless of the magnitude of the input light, the preamplifier 2 may be saturated when the input light increases.

FIG. 6 is a conceptual diagram of the FULL AGC method. The same components as those in FIG. 5 are denoted by the same reference numerals. In this method, the DC voltage source 51 is controlled so that the output amplitude of the equalizing amplifier 53 becomes constant. As the light input increases, the APD bias voltage (the voltage applied to both ends of the APD) Vapd decreases, and the multiplication factor M becomes almost 1 near the maximum reception level, so that the dynamic range of the reception level can be widened. .

On the other hand, since the multiplication factor M has a negative slope with respect to the optical input near the minimum reception level, the S / N ratio becomes constant even when the optical input increases, and the error floor (the curve of the error rate curve) is reduced. ) Occurs. Further, since the negative feedback circuit is configured, there is a problem that the circuit scale becomes large.

In a known example (Japanese Unexamined Patent Publication No. 6-164495), as shown in FIG. 9, an optical receiving circuit is formed by a FULL AGC method, and characteristic data of an APD stored in a memory and temperature by a temperature-sensitive element. By controlling the driving voltage of the APD based on the detection data and the signal level detection data so that the output signal level becomes constant, it is possible to perform fine temperature compensation of the APD with high accuracy corresponding to element variation and the like. I have.

In the system shown in FIG. 9, reference numeral 1 denotes an optical space transmission apparatus as a whole, which drives a laser diode 2 with a predetermined information signal and emits a transmission light beam L1 having a predetermined polarization plane from the laser diode 2. I do. Further, in the optical free space transmission device 1, the transmission light beam L1 is
After the light is converted into a parallel light by, the light is transmitted through the deflection beam splitter 6 and guided to the lens 8. Here, the lens 8 converts the transmission light beam L1 into convergent light and emits the same, and the large-diameter lens 1
0 converts this convergent light into substantially parallel light and emits it.

As a result, in the optical free space transmission apparatus 1, an information signal is transmitted to a transmission target via the transmission light beam L1 having a predetermined polarization plane. Further, in the optical free space transmission device 1, a received light beam L 2 arriving from a desired transmission target is received by a large-diameter lens 10 and guided to a deflection beam splitter 6 via a lens 8. Here, the reception light beam L2 is transmitted from the transmission target such that the polarization plane is orthogonal to the transmission light beam L1, so that the spatial light transmission device 1 divides the reception light beam L2 by the deflection beam splitter 6. The light is reflected and guided to the beam splitter 12. The beam splitter 12 transmits part of the received light beam L2 and emits it to the lens 14, and the lens 14 converts the transmitted light into the APD 16
Focus on

In the optical space transmission apparatus 1, the APD
The 16 output signals are output to a predetermined signal processing circuit for processing, whereby the information signal to be transmitted is received via the reception light beam L2. Further, the beam splitter 12 reflects a part of the received light beam L2 and sends it to the lens 18, and the lens 18 condenses the reflected light L3 by the positioning sensor 20. Here, the positioning sensor 20
Is a position detecting light-receiving element whose output signal changes in accordance with the condensing position of the reflected light L3. In this embodiment, the output signal of the positioning sensor 20 is used as the position detecting circuit 22.
To detect the focus position of the reflected light L3.

Further, in this embodiment, the space optical transmission apparatus 1 inserts a deflecting beam splitter 26 between the beam splitter 12 and the lens 14, and moves the deflecting beam splitter 26 around a predetermined optical axis of the deflecting beam splitter 26. By rotating the angle, the deflection beam splitter 26 is used as an optical attenuator, and the amount of incident light on the avalanche photodiode 16 is maintained at a constant value.

The signal detected by the APD 16 is amplified by a preamplifier 36 and then further amplified by an AGC circuit 38. The output of the AGC circuit 38 is converted into digital data by the A / D converter 40 and supplied to the system control unit 30. The system control unit 30 converts the received digital signal into an analog signal by the D / A converter 42 and supplies the analog signal to the step-down power supply 44. The output of the step-down power supply 44 is
D16. A feedback circuit is formed by the above loop, and the optical signal detected from the APD 16 can be made constant.

However, this method does not solve the problem of the error floor when the light input level is small, as long as the control is performed to keep the output signal level constant. Self-bias method FIG. 7 is a conceptual diagram of the self-bias method. The same components as those in FIG. 5 are denoted by the same reference numerals.

In this system, as shown in FIG. 7, a bias voltage control resistor R1 is connected between a DC voltage source 51 and an APD cathode.
Is controlled by using this voltage drop so that the APD bias voltage Vapd becomes smaller as the light input increases.

FIG. 8 shows an example of the Pin-Iapd characteristic. The vertical axis is Iapd [μA], and the horizontal axis is the optical input power [dBm]. As shown in the figure, since Iapd is small near the minimum reception level, the change of the gain with respect to the optical input in this area is small compared to the FULL AGC method. C connected to the APD is a noise removing capacitor.

If the resistance value is increased to some extent, the multiplication factor M can be set to approximately 1 near the maximum reception level due to a voltage drop. As described above, by setting the DC voltage source 51 so that the optimum multiplication factor is obtained at the minimum reception level and setting the bias voltage control resistor to an appropriate value, the above-described problems near the minimum reception level and the maximum reception level can be achieved. Can be solved.

[0018]

(A) Adjustment of DC voltage source and bias voltage control resistor in self-bias system The self-bias system described above is a multiplication factor M fixed system, FU
The above problems of the LL AGC method can be solved. However, it is necessary to adjust a DC voltage source for the individual variation of the breakdown voltage of the APD and the temperature characteristics and to compensate for the temperature. However, there is a problem that it is necessary to individually set a resistance value.

Adjustment of DC Voltage Source, Temperature Compensation The multiplication factor M of the APD is determined by the relationship between the breakdown voltage Vb and the APD bias voltage (the voltage applied to both ends of the APD) Vapd as shown in the following equation.

M = 1 / {1− (Vapd / Vb) ⁿ } (1) where n is a coefficient determined by the material and structure of the element. V
b has a large individual variation and changes with a certain inclination に 対 し て with respect to the temperature. The multiplication factor is determined by the ratio of Iapd when the APD bias voltage is small and Iapd when the APD bias voltage is sufficiently large.

For this reason, in the self-biasing method, it is necessary to adjust the output voltage Vdd of the DC voltage source 51 so that the multiplication factor becomes optimum near the minimum reception level for each APD. Further, it is necessary to temperature-compensate the voltage Vdd of the output of the DC voltage source 51 with respect to the temperature characteristic の of each APD so that the multiplication factor M becomes constant with respect to the temperature fluctuation.

Setting of Bias Voltage Control Resistor Next, when the DC voltage source 51 is adjusted and the temperature is compensated as described above and the optical input is increased beyond the vicinity of the minimum reception level, the APD current Iapd increases. Accordingly, Vapd becomes smaller due to a voltage drop in the bias voltage control resistor R1. Iapd and Vapd at a certain optical input Pin can be obtained from the following equations.

Iapd = S · M · Pin (2) where S is the APD light receiving sensitivity [A / W] Vapd = Vdd− (R1 + R0) · Iapd (3) where the bias voltage of the self-bias method shown in FIG. When the control resistor R1 is large, Vapd near the maximum reception level becomes too small, and the frequency band of the APD deteriorates. vice versa,
When the resistance value of R1 is small, M at the maximum reception level does not become sufficiently small, so that Iapd exceeds the allowable maximum value of the input current of the preamplifier 52, and the preamplifier 52 saturates.
Waveform deterioration occurs.

FIGS. 10A and 10B are diagrams showing an example of the Pin-Vapd characteristic, wherein FIG. 10A shows the overall characteristic and FIG. 10B shows an enlarged view.
(B) shows the enlargement of the area A surrounded by the wavy line in (a). The vertical axis represents Vapd, and the horizontal axis represents the optical input power Pin. When R1 is large, as the optical input power Pin increases, the AP
The voltage Vapd applied to D is small. In (b), an area B indicates an APD band degradation limit area.

FIG. 11 is a diagram showing an example of the Pin-M characteristic. The vertical axis represents the multiplication factor M, and the horizontal axis represents the optical input power Pin. (A) is an enlarged view of the whole, and (b) is an enlarged view of a region C surrounded by a wavy line of (a). When the resistance value of R1 is small, M near the maximum reception level does not become sufficiently small.
apd exceeds the allowable maximum value of the input current of the preamplifier 52,
The waveform of the output of the preamplifier 52 deteriorates. FIG.
The maximum value of the load resistance R0 can be determined by the capacity of the APD and the required frequency band.

As described above, in the self-bias method, A
Due to individual variations in the breakdown voltage of PDs and temperature characteristics, it is difficult to simplify adjustment of an optical receiving module (optical receiving unit), and to make components common and common.

The present invention has been made in view of such a problem, and a general-purpose combination of an optical receiving module and an APD bias voltage control unit is possible. It is an object of the present invention to provide an APD bias voltage control circuit capable of reducing the size of a module and sharing the structure of a PIN light receiving module.

[0028]

(1) FIG. 1 is a block diagram showing the principle of the present invention. The same components as those in FIG. 7 are denoted by the same reference numerals. In the figure, reference numeral 60 denotes an optical signal (Opt I
n), the optical receiving unit (optical receiving module) 70 for converting the received signal into an electric signal and outputting output data,
This is an APD bias voltage control unit that applies an optimal bias voltage to an APD of 0. The light receiving unit 60 and the APD bias voltage control unit 70 are separately configured.

In the APD bias voltage controller 70,
Reference numeral 71 denotes a DC voltage source whose output voltage can be controlled, R10 is connected to the DC voltage source 71, and its resistance value is varied by an external signal. Is a CPU for performing various controls. The CPU 72 includes a DC voltage source 71 and a variable resistor R
10 is given a control signal.

In the light receiving section 60, reference numeral 61 denotes a memory in which a breakdown voltage and its temperature gradient are stored. The breakdown voltage Vb and the temperature gradient Γ read from the memory 61 are given to the CPU 72. The optical receiver 60 includes a temperature sensor 62,
Output the ambient temperature of D.

With this configuration, the CPU 72 compensates for the optimum reception characteristics based on the ambient temperature and the breakdown voltage of the APD at that time so that the multiplication factor M is constant with respect to temperature fluctuation. The DC voltage source 71 is controlled to the set voltage value, and M and Vapd near the maximum reception level.
The variable resistor R10 is set to a resistance value that optimizes the optical receiving module and the APD bias voltage control unit 7.
APD bias voltage control that can be used in a versatile combination with the APD bias voltage control unit 70 and allows the optical receiving unit 60 to be miniaturized by externally attaching the APD bias voltage control unit 70 and that allows the PIN element optical receiving unit 60 to have a common structure. A circuit can be provided.

The APD bias voltage control unit 70
Since it is automatically controlled based on the individual information of the light receiving unit 60 combined therewith, any combination of the light receiving unit 60 and the APD bias voltage control unit 70 is possible, and the individual break voltage of the APD is Optimum receiving characteristics can be obtained without individually adjusting the optical receiving unit 60 with respect to variations and temperature characteristics.

(2) According to a second aspect of the present invention, in the optical receiving unit 60, the APD connected to the bias voltage controlling variable resistor R10, the breakdown voltage value of the APD, and its temperature characteristic data are stored. Memory, a temperature sensor for detecting a temperature around the APD, an amplifier for amplifying an electric signal generated in the APD, and an identification regenerator for outputting data and a clock from an output of the amplifier. It is characterized by.

With this configuration, the ambient temperature data T required for the bias voltage control and the breakdown voltage Vb at that time can be given to the CPU 72, and the bias voltage of the APD can be set optimally.

(3) In the invention according to claim 3, the temperature sensor is installed at a place thermally separated from the APD,
The CPU 72 of the bias voltage control unit 70 converts the temperature detection data into an APD element temperature, and receives the APD element temperature based on this value, the APD breakdown voltage value read from the optical reception unit, and its temperature characteristic data. A with optimum characteristics
It is characterized in that the voltage value of the PD bias voltage and the resistance value of the bias voltage control variable resistor are calculated, and the DC voltage source and the bias voltage control variable resistor are controlled to these values.

With this configuration, the temperature sensor can be connected to the AP.
Even if it is set apart from D, it is converted into the APD element temperature, and from the breakdown voltage Vb at that time, the CPU 72
The bias voltage of D can be set optimally.

In the present invention, the optical receiver and the APD
In the configuration with the bias voltage control unit, the CPU and the variable resistor for controlling the bias voltage are installed in the optical receiving unit.
U is the breakdown voltage value of the APD and its temperature characteristic data stored in advance in the memory, and the APD by the temperature sensor.
Based on the detected data of the element temperature, the resistance of the bias voltage control variable resistor is automatically set so that the receiving characteristic of the optical receiving unit is optimal, and the APD bias that the receiving characteristic of the optical receiving unit is optimal The voltage value of the voltage is output, and the APD bias voltage control unit can optimally set the bias voltage of the APD by automatically controlling the DC voltage source to this value.

Further, according to the present invention, the breakdown voltage of the APD and its temperature characteristic, the detection output of the temperature sensor,
If the DC voltage source control signal and the bias voltage control variable resistor setting signal are discrete digital signals,
The CPU 72 can optimally set the bias voltage of the APD based on these digital signals.

[0039]

FIG. 2 is a block diagram showing a first embodiment of the present invention. 1, 6 and 7 are denoted by the same reference numerals. In the light receiving unit (light receiving module) 60, reference numeral 61 denotes a memory in which temperature characteristic data and a corresponding breakdown voltage are stored;
This is a temperature sensor provided around the PD. C is APD
Is a capacitor for removing noise provided on the cathode side of the. The variable resistance R10 of the APD bias voltage control unit 70 is connected to the cathode side of the APD, and the resistance R0 is connected to the anode side.

Reference numeral 52 denotes a preamplifier connected to the anode side of the APD; 53, an equalizing amplifier receiving the output of the preamplifier 52; Is a discriminating regenerator that outputs the data to the discriminator. 6
Reference numeral 1 denotes a memory in which the relationship between the temperature characteristic data and the breakdown voltage is stored. In the memory 61, the temperature characteristic data Γ and the breakdown voltage Vb can be set. The output of the memory 61 enters the CPU 72 of the APD bias voltage controller 70. Reference numeral 62 denotes a temperature sensor arranged around the APD. The operation of the circuit thus configured will be described as follows.

In the memory 61 built in the optical receiving unit 60,
The individual information (temperature characteristic Γ, breakdown voltage Vb) of the mounted APD is written. When purchasing an APD, the individual information is attached to each APD, and the information may be written. These temperature characteristics Γ and breakdown voltage Vb are given to CPU 72. On the other hand, the temperature sensor 62 detects the temperature Tapd of the APD and
Give to 2.

In the APD bias voltage control unit 70, Vb and APD output from the memory 61 of the light receiving unit 60 are output.
Receiving the ambient temperature Tapd, the CPU 72 calculates the optimum voltage value of Vdd and the resistance value of the variable resistor R10, and outputs a DC voltage control signal Vdd Cont and a bias voltage control resistance setting signal R10 Cont to output the DC voltage. The source 71 and the resistance of the variable resistor R10 are controlled.

As a result, based on the ambient temperature and the breakdown voltage of the APD at that time, the CPU 72 calculates the voltage value compensated so that the reception characteristics are optimized and the multiplication factor M is constant with respect to temperature fluctuation. And the variable resistor R10 is set to a resistance value that optimizes M and Vapd near the maximum reception level, so that the general use of the optical reception unit 60 and the APD bias voltage control unit 70 is performed. APD that can be combined in various ways, makes it possible to reduce the size of the optical receiving module by externally attaching the APD bias voltage control unit 70, and also to make the structure of the PIN element optical receiving module common
A bias voltage control circuit can be provided.

The APD bias voltage control unit 70
Since it is automatically controlled based on the individual information of the light receiving unit 60 combined therewith, any combination of the light receiving unit 60 and the APD bias voltage control unit 70 is possible, and the individual break voltage of the APD is Optimum receiving characteristics can be obtained without individually adjusting the optical receiving unit 60 with respect to variations and temperature characteristics.

FIG. 3 is a block diagram showing a second embodiment of the present invention. The same components as those in FIG. 2 are denoted by the same reference numerals. In this embodiment, the temperature sensor 62 is not the optical receiver 60 but the APD bias voltage controller 70.
Has moved to the side. Other configurations are the same as those in FIG. The operation of the circuit thus configured will be described as follows.

When the temperature sensor 62 moves to the APD bias voltage control unit 70, the CPU 72 calculates a temperature difference between the output Ta of the temperature sensor 62 and the actual APD element temperature Tapd in advance, and calculates Tapd from Ta based on this. The temperature compensation of Vdd is performed by conversion. After Tapd is calculated, the process is the same as that of the embodiment shown in FIG.

That is, in the APD bias voltage control unit 70, Γ from the optical receiving unit 60 output from the memory 61,
In response to Vb, the CPU 72 calculates the optimum voltage value of Vdd and the resistance value of the variable resistor R10 from Tapd, Γ, and Vb, and outputs the DC voltage control signal Vdd Cont and the bias voltage control resistance setting signal R10 Cont. Then, the DC voltage source 71 and the resistance value of the variable resistor R10 are controlled.

As a result, based on the ambient temperature and the breakdown voltage of the APD at that time, the CPU 72 obtains a voltage value compensated such that the reception characteristics are optimized and the multiplication factor M is constant with respect to temperature fluctuation. And the variable resistor R10 is set to a resistance value that optimizes M and Vapd near the maximum reception level, so that the general use of the optical reception unit 60 and the APD bias voltage control unit 70 is performed. APD that can be combined in various ways, makes it possible to reduce the size of the optical receiving module by externally attaching the APD bias voltage control unit 70, and also to make the structure of the PIN element optical receiving module common
A bias voltage control circuit can be provided.

FIG. 4 is a block diagram showing a third embodiment of the present invention. The same components as those in FIG. 2 are denoted by the same reference numerals. This embodiment is different from the embodiment shown in FIG. 2 in that a variable resistor R10 and a CPU 72 are provided on the optical receiving unit 60 side. The output of the temperature sensor 62 provided around the APD enters the CPU 72, and the temperature characteristic ブ and the breakdown voltage Vb stored in the memory 61 are read and entered into the memory 61. Other configurations are the same as those in FIG. In this embodiment, the AP
The D bias voltage control unit 70 includes only the DC voltage source 71 and receives the voltage control signal Vdd Cont from the optical receiving unit 60. The operation of the circuit thus configured will be described as follows.

In the memory 61 built in the optical receiving unit 60,
The individual information (temperature characteristic Γ, breakdown voltage Vb) of the mounted APD is written. These temperature characteristics Γ and breakdown voltage Vb are given to CPU 72. On the other hand, the temperature sensor 62 detects the temperature Tapd of the APD and gives it to the CPU 72.

In response to the temperature characteristic Γ output from the memory 61, the breakdown voltage Vb and the ambient temperature Tapd of the APD, the CPU 72 determines the optimum voltage value of Vdd and the variable resistor R1.
0 and calculate the DC voltage control signal Vdd Con.
t, the bias voltage control resistor setting signal R10 Cont is output to control the resistance values of the DC voltage source 71 and the variable resistor R10.

As a result, based on the ambient temperature and the breakdown voltage of the APD at that time, the CPU 72 obtains a voltage value compensated such that the reception characteristics are optimized and the multiplication factor M is constant with respect to temperature fluctuation. And the variable resistor R10 is set to a resistance value that optimizes M and Vapd near the maximum reception level, so that the general use of the optical reception unit 60 and the APD bias voltage control unit 70 is performed. APD that can be combined in various ways, makes it possible to reduce the size of the optical receiving module by externally attaching the APD bias voltage control unit 70, and also to make the structure of the PIN element optical receiving module common
A bias voltage control circuit can be provided.

In the above embodiment, the breakdown voltage Vb, the temperature Tapd of the APD, the output Ta of the temperature sensor 62, the DC voltage source control signal Vdd Cont, and the variable resistance control signal R10 Cont are digital values. Alternatively, it may be an analog value such as a voltage value.

The above-mentioned memory 61 may be an EEPROM or a FLASH memory. Further, the above-described variable resistor R10 may be an electronic volume or a field effect transistor (FET).

The temperature sensor 62 may be a diode or a thermistor. According to the present invention, A
By controlling the PD bias voltage control unit, a general-purpose combination of the optical receiving module and the APD bias voltage control unit becomes possible, and the optical receiving unit (optical receiving module) by externally attaching the APD bias voltage control unit , And the structure can be shared with the PIN element optical receiving module. In the conventional self-bias method,
In addition to adjusting and compensating the DC voltage source for individual variations in APD breakdown voltage and temperature characteristics,
For the bias voltage control resistors, it is necessary to individually set the resistance values. However, according to the present invention, these automatic adjustments can be performed, and the adjustment of the optical receiving module can be greatly simplified.

(Supplementary Note 1) In an APD bias voltage control circuit that controls a bias voltage of an avalanche photodiode (APD) by a self-bias method, receives an optical signal, converts it into an electric signal, and outputs output data. Unit and an APD bias voltage control unit for providing an optimal bias voltage to the APD of the optical receiving unit, wherein the APD bias voltage control unit comprises: a DC voltage source capable of controlling its output voltage; Connected to a voltage source,
It comprises a variable resistor for bias voltage control whose resistance value is varied by an external signal, and a CPU for performing various controls. The CPU has a breakdown voltage value of the APD stored in a memory of the optical receiving unit. An APD bias voltage control circuit which reads out the temperature characteristic data and controls the DC power supply and the bias voltage control variable resistor so as to optimize the reception characteristic of the optical receiver.

(Supplementary Note 2) The light receiving unit includes an APD connected to the bias voltage controlling variable resistor, a memory for storing a breakdown voltage value of the APD and its temperature characteristic data, and a temperature around the APD. 2. The APD according to claim 1, further comprising: a temperature sensor for detecting an APD, an amplifier for amplifying an electric signal generated in the APD, and an identification regenerator for outputting data and a clock from an output of the amplifier. Bias voltage control circuit.

(Supplementary Note 3) The temperature sensor is installed at a location that is thermally separated from the APD, and the CPU of the APD bias voltage control unit converts the temperature detection data into an APD element temperature. Based on the breakdown voltage value of the APD read from the unit and the temperature characteristic data thereof, calculate the voltage value of the APD bias voltage and the resistance value of the variable resistor for controlling the bias voltage at which the receiving characteristic of the optical receiving unit is optimal, The APD bias voltage control circuit according to claim 2, wherein a DC voltage source and a bias voltage control variable resistor are controlled to these values.

(Supplementary Note 4) In the configuration of the optical receiving unit and the APD bias voltage control unit, the CPU and the bias voltage controlling variable resistor are installed in the optical receiving unit.
Based on the breakdown voltage value of the APD and its temperature characteristic data previously stored in the memory and the data on the temperature of the APD element detected by the temperature sensor, the variable resistor for controlling the bias voltage is adjusted so that the reception characteristic of the optical receiver becomes optimum. APD that automatically sets the resistance value and optimizes the receiving characteristics of the optical receiver
The APD bias voltage control circuit according to claim 1, wherein a voltage value of the bias voltage is output, and the APD bias voltage control unit automatically controls the DC voltage source to this value.

(Supplementary Note 5) The breakdown voltage of the APD and its temperature characteristic, the detection output of the temperature sensor, the DC voltage source control signal, and the bias voltage control variable resistor setting signal are discrete digital signals. 5. The APD bias voltage control circuit according to any one of supplementary notes 1 to 4.

[0061]

As described above, according to the present invention,
The following effects can be obtained. (1) According to the first aspect of the present invention, the size of the optical receiving unit is reduced by externally attaching the APD bias voltage control unit, and further, the PI
It is possible to provide an APD bias voltage control circuit that can share the structure of the N-element light receiving unit.

Further, since the APD bias voltage control section is automatically controlled based on the individual information of the optical receiving section combined therewith, any combination of the optical receiving section and the APD bias voltage control section becomes possible. Further, it is possible to obtain an optimum receiving characteristic without individually adjusting the optical receiving unit with respect to the individual variation and the temperature characteristic of the break voltage of the APD.

(2) According to the second aspect of the present invention, the ambient temperature data T required for bias voltage control and the breakdown voltage Vb at that time can be given to the CPU.
The bias voltage of D can be set optimally.

(3) According to the third aspect of the present invention, even if the temperature sensor is installed at a distance from the APD, the temperature sensor is converted into the temperature of the APD element and the CP is calculated from the breakdown voltage Vb at that time.
U can optimally set the bias voltage of the APD.

In the present invention, the receiving characteristic of the optical receiving unit is optimized based on the breakdown voltage value of the APD and its temperature characteristic data stored in the memory in advance and the detection data of the APD element temperature by the temperature sensor. The resistance value of the variable resistor for controlling the bias voltage is automatically set, and the voltage value of the APD bias voltage at which the receiving characteristic of the optical receiving unit is optimal is output. On the other hand, the APD bias voltage controlling unit By automatically controlling the voltage source, the bias voltage of the APD can be set optimally.

Also, according to the present invention, the breakdown voltage of the APD and its temperature characteristic, the detection output of the temperature sensor,
If the DC voltage source control signal and the bias voltage control variable resistor setting signal are discrete digital signals,
The CPU can optimally set the bias voltage of the APD based on these digital signals.

As described above, according to the present invention, a general-purpose combination of the optical receiving module and the APD bias voltage control section is possible, and the optical receiving module can be miniaturized by externally attaching the APD bias voltage control section. It is possible to provide an APD bias voltage control circuit capable of sharing the structure of the PIN element light receiving module.

[Brief description of the drawings]

FIG. 1 is a principle block diagram of the present invention.

FIG. 2 is a block diagram illustrating a first embodiment of the present invention.

FIG. 3 is a block diagram showing a second embodiment of the present invention.

FIG. 4 is a block diagram showing a third embodiment of the present invention.

FIG. 5 is a conceptual diagram of a multiplication factor M fixing method.

FIG. 6 is a conceptual diagram of a FULL AGC scheme.

FIG. 7 is a conceptual diagram of a self-bias method.

FIG. 8 is a diagram illustrating an example of a Pin-Iapd characteristic.

FIG. 9 is a diagram showing a known example of an optical space transmission device.

FIG. 10 is a diagram illustrating an example of a Pin-Vapd characteristic.

FIG. 11 is a diagram illustrating an example of a Pin-M characteristic.

[Explanation of symbols]

 Reference Signs List 60 light receiving unit 61 memory 70 APD bias voltage control unit 71 DC voltage source 72 CPU R10 bias voltage control resistor (variable resistor)

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification FI FI Theme Court ゛ (Reference) H03F 3/08 (72) Inventor Yukiji Fuse 4-3-1 Kita-Nanajo-Nishi 4-chome, Kita-ku, Sapporo, Hokkaido, Japan Fujitsu F-term (reference) in Hokkaido Digital Technology Co., Ltd.

Claims (3)

[Claims] 1. A method of controlling a bias voltage of an avalanche photodiode (APD) by a self-bias method.
In a PD bias voltage control circuit, an optical receiving unit that receives an optical signal input, converts the optical signal into an electric signal, and outputs output data, and an AP that applies an optimal bias voltage to an APD of the optical receiving unit
A D bias voltage control unit is separately provided; the APD bias voltage control unit is connected to the DC voltage source capable of controlling its output voltage; and the resistance value is varied by an external signal. A variable resistor for controlling a bias voltage; and a CPU for performing various controls. The CPU includes an AP stored in a memory of an optical receiving unit.
An APD bias voltage reading out the breakdown voltage value of D and the temperature characteristic data thereof, and controlling the DC power supply and the variable resistor for bias voltage control so as to optimize the reception characteristic of the optical receiver. Control circuit. 2. An APD connected to the bias voltage controlling variable resistor, wherein:
A memory in which a breakdown voltage value of the APD and its temperature characteristic data are stored; a temperature sensor for detecting a temperature around the APD; an amplifier for amplifying an electric signal generated in the APD; and an output from the amplifier. 2. The APD bias voltage control circuit according to claim 1, comprising an identification regenerator for outputting data and a clock. 3. The temperature sensor is installed at a location that is thermally separated from the APD, and a CPU of the APD bias voltage control unit.
Converts the temperature detection data into an APD element temperature, and based on this value, the breakdown voltage value of the APD read from the optical receiving unit and its temperature characteristic data, sets the APD bias at which the receiving characteristic of the optical receiving unit is optimal. 3. The APD bias voltage control according to claim 2, wherein the voltage value of the voltage and the resistance value of the bias voltage control variable resistor are calculated, and the DC voltage source and the bias voltage control variable resistor are controlled to these values. circuit.